The present invention is directed to the fields of energy storage system (ESS) management systems, electrical demand charge management, and related fields.
With the electrical demand of a customer in today's electrical distribution grid rising at a restless pace, electricity providers have had to find ways to prevent or discourage overloading of the transformers, feeders, and mains across their distribution networks. In some areas, utilities have adopted the practice of billing demand charges, which are electricity bills assessed in proportion to the highest consumption drawn by a customer during a billing cycle (e.g., over one month). When calculating demand charges, utility providers typically measure facility energy usage over short predetermined time periods (e.g., every ten or fifteen minutes), calculate and store the average level of demand for each of these periods, and then generate the demand charge billed to the customer based on the highest level of averaged consumption experienced by the end of the billing cycle. Thus, even brief spikes in demand can have a dramatic effect on demand charges.
Demand charge management is the practice of reducing demand charges. It usually involves reducing the peak electrical load drawn at a site at times when utility costs are high or when consumption at the site is high, thereby reducing the averaged demand across sections of a billing cycle. Consumers have adopted peak mitigation and peak shaving techniques to manage demand charges wherein an ESS is discharged to the grid at the moment when an excessive increase in the electrical demand is encountered in order to offset or nullify the contribution of the increased demand at that time to the final demand averages calculated by the utility provider when determining a demand charge.
Elevated demand periods may be classified as spikes and plateaus. A spike in demand is an increase in demand that is short, perhaps a few seconds or minutes long, that is in excess of the highest demand value (or highest average demand value) previously experienced during that billing cycle. A plateau in demand is an extended period of increased consumption exceeding that highest demand value (or averaged demand value), such as a peak in consumption that can last for many minutes or hours.
Existing peak mitigation systems are inefficient when they need to address both spikes and plateaus of consumption. If a peak in consumption is experienced, present systems immediately discharge the ESS to diminish the peak to avoid causing new demand charges. Depending on the ESS capacity of the system, this technique is most effective when brief demand spikes are encountered. If an extended plateau is encountered and the ESS capacity (or state of charge) is insufficient to mitigate the entire plateau, the system will run out of energy while mitigating and at least part of the plateau will go unmitigated. Alternatively, a low-capacity system may be discharged at a lower rate when a peak is experienced in order to allow the system to discharge for longer before depleting, but if the magnitude of the peak is much higher than the average consumption at the site, the low-rate discharge may not produce enough mitigation to keep the peak from producing an increased demand charge.
Because of the nature of demand charge calculation, even brief unmitigated peak periods can result in extreme demand charges. Increasing the available ESS capacity is a logical way to avoid this kind of unmitigated plateau scenario, but ESS capacity can be very expensive per kilowatt, especially when the ESS is a battery system. Furthermore, although large ESS capacity systems can service plateaus in consumption without allowing peaks to go unmitigated, they are oversized and not cost-effective for mitigating consumption spikes.